9995c45ef6
The ``python-apt`` package is a wrapper around the ``apt`` C++ library which is tightly connected to the version of the distribution it is shipped on. This in turn makes it incredibly hard to distribute as a wheel for a charm that supports a large span of distro versions. We do not want to rely on system installed Python packages but distribute the direct charm dependencies as part of the charms wheelhouse. As the span of distributions we need to support with reactive charms widens we will run into compability problems with the current model. For further reference see discussion in LP: #1824112 and juju-solutions/layer-basic#135 Change-Id: I292dcba7cf2de18e53ae80339d07c6e1fe5c90fc
59 lines
2.3 KiB
Python
59 lines
2.3 KiB
Python
import json
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import hashlib
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import charmhelpers.core as core
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# TODO(AJK): Once this is in charms.reactive, drop it here and just reference
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# the charms.reactive version.
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# NOTE(AJK): that we are breaking the camalcase rule as this is acting as a
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# context manager, which doesn't look like a 'class'
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class is_data_changed(object):
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""" Check if the given set of data has changed since the previous call.
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This works by hashing the JSON-serialization of the data. Note that, while
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the data will be serialized using ``sort_keys=True``, some types of data
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structures, such as sets, may lead to false positivies.
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The hash of the changed data WON'T be stored until a successful exit of the
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context manager. This means if the code in the scope of the context
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manager raises an exception, then the data won't be changed and the next
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check will leave it unchanged. This is to allow for recovery from errors.
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Usage:
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with is_data_changed() as changed:
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charm_instance.some_method()
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"""
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def __init__(self, data_id, data, hash_type='md5',
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no_change_on_exception=True):
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"""Initialise the context manager:
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@param data_id: <String> the unique name for this data
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@param data: a JSON serialisable data object.
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@param hash_type: A hashing function available from hashlib
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default='md5'
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@param no_change_on_exception: if an exception is thrown in the managed
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code then the new hash is not persisited.
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"""
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self.data_id = data_id
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self.data = data
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self.hash_type = hash_type
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self.no_change_on_exception = no_change_on_exception
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def __enter__(self):
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"""with statement as returns boolean"""
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self.key = 'charms.openstack.data_changed.{}'.format(self.data_id)
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alg = getattr(hashlib, self.hash_type)
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serialized = json.dumps(self.data, sort_keys=True).encode('utf8')
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old_hash = core.unitdata.kv().get(self.key)
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self.new_hash = alg(serialized).hexdigest()
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return old_hash != self.new_hash
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def __exit__(self, e_type, *_):
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# If no exception, then store the new hash.
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if e_type is None or not self.no_change_on_exception:
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core.unitdata.kv().set(self.key, self.new_hash)
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# re-raise the exception, if there was one.
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return False
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